Hot melt adhesives are widely used for various commercial and industrial applications such as product assembly and packaging. Such hot melt adhesives are applied to a substrate while in its molten state and cooled to harden the adhesive layer.
Most commercially available hot melt adhesives require temperatures of 350° F. or greater to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. The need for such elevated temperatures is not without problems. The high temperatures increase operators risks with respect both to burns and to inhalation of residual volatiles. In addition, the high temperatures require more energy, placing greater demands on the manufacturing facility.
Adhesive formulations, which can be applied at temperatures below 300° F., can be prepared using low polymer/elastomer content or low molecular weight components or a high wax content. Although these formulations achieve a low application viscosity, there is a resulting loss of adhesive properties such as toughness, heat resistance, and sometimes, specific adhesion to a substrate. While the formulation of poly(ethylene-vinylacetate)-based adhesives having high heat resistance has been in addressed in the art, see, e.g., U.S. Pat. No. 6,117,945, lower application temperature (e.g., less than 300° F.) thermoplastic elastomer-based adhesives which provide toughness, strength, and specific adhesion on a desired substrate have not been achieved.
Accordingly it would be desirable to have thermoplastic elastomer-based adhesives that exhibit good bond strength with exceptional toughness, tensile strength and application viscosity, even if prepared with low molecular weight components for application at low temperatures. The current invention addresses this need in the art.